1. Field of the Invention
The present invention relates to a method and a device for holding a sheet-like workpiece by rolling out the sheet-like workpiece wound in a roll to hold a part thereof on a flat table. The invention is suitably applicable to a laser machining apparatus for machining a flexible printed board for example.
2. Description of the Prior Art
As a machining apparatus for machining a sheet-like workpiece, there has been known a laser machining apparatus having, successively, an unwinding unit for unwinding a non-machined material wound in a roll, a machining unit having a machining section (laser head) for drilling the non-machined material and a take-up unit for taking up the finished material in a roll as disclosed in Japanese Patent Laid-Open No. 2004-195510 for example. The laser machining apparatus also includes a machining table disposed so as to be movable relative to a main frame of the machining apparatus such that a plurality of blocks of the non-machined material can be moved and positioned in a longitudinal direction of the material for machining by the machining section. The laser machining apparatus also includes clamp means disposed in a body of the machining table and operates so as to clamp the non-machined material with respect to the machining table when the machining table moves from a starting position to an ending position and to release the non-machined material from the machining table when the machining table returns to the starting position. Moreover, the laser machining apparatus includes relative position fixing means that operate to fix relative positions of the non-machined material to the machining apparatus before releasing the non-machined material from the clamp means when the machining table reaches the end position and so as to release the fixed state of the relative position of the non-machined material to the machining apparatus after clamping the non-machined material with the clamping means when the machining table returns to the starting position.
This technology makes it possible to prevent the position of a printed board, i.e., a sheet-like workpiece, from deviating from the laser head and hence improves machining efficiency.
It is noted that the sheet-like printed board is often positioned on the machining table by applying a slight tensile force between a feed roll and a take-up roll, and by fixing the printed board on the machining table using suction or fixtures such as a clamper.
There has also been known a laser machining apparatus having at least a pair of clamps for holding both ends of a material to be machined and a tensioning unit for applying bias between the pair of clamps in a direction of relatively separating from each other to apply a tensile force to the non-machined material as disclosed in Japanese Patent Laid-Open No. 1998-296473 for example.
Since this technology allows the material to be kept flat even if it is apt to curl, it allows machining accuracy to be improved.
Moreover, in laser drilling a printed board on which copper foil is provided, etching is carried out before the drilling and a thickness of the printed board becomes uneven due to etching. Therefore, the printed board wound in a roll after etching causes wrinkles formed almost in parallel with a running direction the printed board.
The wrinkles formed almost in parallel with the running direction are unable to be removed even if a tensile force is applied in the running direction of the printed board. Therefore, the printed board on which etching process has been carried out is held on the table while having the wrinkles.
Although no hole can be machined, causing defective machining, at the wrinkled part because it is out of focus in case of laser machining, no consideration has been given to the wrinkles running almost in parallel with the running direction of the sheet-like workpiece in Japanese Patent Laid-Open Nos. 2004-195510 and 1998-296473.
Accordingly, it is an object of the invention to provide a method and a device capable of holding a sheet-like workpiece on a table without wrinkles.
This object may be achieved through the combination of features described in independent claims of the invention. Dependent claims thereof specify preferable embodiments of the invention.